The invention relates to improvements in catheters in general, and more particularly to improvements in catheters with expansible distal ends.
Catheters with expansible distal ends are used to open an occlusion (stenosis) in a blood vessel or in the cavity or passage of another part of an animal body. As a rule, or in many instances, the expansible portion of a catheter is a balloon which is introduced into an occlusion in collapsed (non-inflated) condition and is thereupon inflated to thereby open the occlusion. When the inflating step is completed, the balloon is deflated and is ready to be extracted from the opened occlusion and from the animal body.
A drawback of presently known catheters which employ inflatable and deflatable balloons is that a balloon is not likely to invariably open an occlusion or to open an occlusion to a desired extent because its material is too soft and hence too yieldable so that it cannot dislodge a relatively hard region or portion of an occlusion. The only presently known proposal to overcome such problems is to raise the pressure of fluid medium which is used to inflate the balloon. Such solution is not satisfactory because a balloon will expand around a relatively hard region of an occlusion and will not change the position of the hard portion or region at all or only to a negligible extent. Thus, the opened or partly opened occlusion will continue to include one or more hard regions which project well into the body cavity (e.g., into the passage within a blood vessel) with attendant likelihood of renewed occlusion after a relatively short period of time. As a rule, it is desirable that an opened or expanded occlusion exhibit a smooth internal surface.
Therefore, many specialists in the relevant field employ catheters which are actually drilling, milling or boring tools in that their distal ends comprise implements which are designed to remove tissue and/or other material in the region of a stenosis and to thus open the occlusion to the flow of body fluids. Removal of material from a stenosis is often undedesirable and plain dangerous because the removed material migrates in the body cavity and is likely to agglomerate and clog a blood vessel or the like.
U.S. Pat. No. 4,793,359 to Sharrow discloses a transluminal angioplasty catheter wherein the balloon at the distal end of the catheter serves as a means for properly positioning a laser which can direct a hot spot of laser energy onto an occlusion. A drawback of the proposal of Sharrow is that the treatment with laser involves removal of material from an occlusion with the aforediscussed undesirable consequences.
Published European patent application No. 0 246 998 of Porath-Furedi discloses a cardiac balloon catheter which is provided with a bypass conduit to establish a flow path for the blood bypassing the balloon when the balloon is inflated. This publication further discloses a self-supporting split sleeve which is expanded by the balloon and remains implanted in the blood vessel upon completed deflation and removal of the catheter and its balloon. The expanded sleeve has detent means or is otherwise designed to ensure that it remains in the blood vessel, i.e., that it cannot be extracted with the deflated balloon. The purpose of the implanted sleeve is to prevent closing or partial closing of an occlusion. A drawback of such proposal is that a rather large foreign body is left in the blood vessel and is likely to change its position after a certain interval of time, either gradually or abruptly, with attendant danger of clogging and/or injury to the blood vessel.
U.S. Pat. No. 4,796,629 to Grayzel discloses a stiffened dilation balloon catheter wherein certain isolated portions of the inflatable balloon are stiffened to ensure that the balloon can resist deformation of such isolated portions when it is inflated during the treatment procedure. The patented catheter is more likely to dislodge certain hard regions of an occlusion; however, the dislodging action is not reliable because not all portions (the patent refers to isolated reinforced portions) of the balloon are reinforced or stiffened so that hard regions of an occlusion can penetrate between neighboring stiffened portions of the balloon when the latter is expanded within an occlusion. The entire balloon cannot be stiffened because this would prevent its inflation and expansion in response to admission of a supply of pressurized fluid.
Published European patent application No. 0 206 553 of Streatfield et al. discloses an expansible cannula for introduction of instruments, scopes or tubing into a body cavity or organ. The cannula is not designed to open, nor is it capable of opening, an occlusion in a blood vessel or in another body portion or organ. On the contrary, the inventors state that their cannula can be used for placement of catheters into the biliary or urogenital system for drainage.